plus.key.addEventListener("backbutton",onback);
function onback(){
	app.$toast("再次点击退出");
	removeEventListener();
	localStorage.setItem("kdn3",0);
	setTimeout(function(){
		plus.key.addEventListener("backbutton",onback);
		
	},3000);
	
}
function removeEventListener(){
		plus.key.removeEventListener("backbutton",onback)
	}